- two coins that have a "heads" and
a "tails" side
- a partner
- paper to record data
- a pen or pencil

Scientific Background of
Experiment:

A gene is something that makes us who we are
by determining what we act and look like. Genes are passed down from
parents to their children. Some examples of genes are the color of
our hair and eyes as well as how tall we will be. Different gene
expressions, the outside appearance, like blonde hair or brown hair,
happen because each gene has different alleles, which are the parts
of genes that are passed down by each parent. There are two types of
alleles &endash; one that gives a more common expression of the gene,
which is called dominant, and one that occurs less often, the
recessive allele. The dominant allele is usually shown as a capital
letter, like B, and the recessive is shown as a lower-case letter,
like b. Because one allele is given by each parent, every person has
two alleles for every gene. For example: if B, the dominant allele,
gives someone brown eyes, and b, the recessive allele, gives someone
blue eyes, a person with the alleles "BB" or "Bb" would have brown
eyes &endash; because the capital B is dominant over the lower-case
b. Someone with the alleles "bb" would have the recessive expression
of the gene being passed down. In this case, it might represent
someone who has blue eyes. If you think about it, there are a lot
less people with blue eyes because it is the less common expression
due to its recessive alleles.

A way that scientists can predict &endash;
or guess &endash; what genes someone will have is to look at the
different alleles that they parents have. A Punnett Square is used to
show the results if the two parents having children. If one parent
has both dominant alleles and the other has both recessive, the cross
of the parents would look like this:

RR X rr

R R

Rr Rr

Rr Rr

r

r

Here, each of the offspring, or the
new combinations of alleles that were made, would each have brown
eyes because they have one of each allele, and the dominant allele,
R, will determine the expression of the gene. When two of these
offspring are tested, the following cross will result:

Rr X Rr

R r

RR Rr

Rr rr

R

r

In this case, the result of the cross is
slightly different. Can you guess how many of the offspring will have
brown eyes? How about blue eyes? If you guessed that three out of the
four would have brown eyes, you were right! The reason is that three
of the four offspring have the dominant allele, R, as a part of the
gene. This means that the one offspring left that did not have the
dominant allele must be blue eyed because it produces a recessive
gene. The Gene frequency is a number that tells how often the gene
occurs or is expressed in the individuals of a population.

In a population, or a group of the same kind
of animals or plants, there are certain numbers of individuals that
will have the dominant and recessive genes that are described here.
This is the concept of Probability. Probability is measuring the
chance that something will happen, or in this case, the chance that a
certain individual will have a certain gene. Scientists can use
probability to determine how many organisms in a population will have
the genes that they are studying. In this experiment, we will see how
probability can be helpful to guess the number of organisms with the
same gene or expression of a gene in a certain group. This will
demonstrate the concept of the Punnett square as well as show the
different possible combinations of alleles that can occur to produce
different genes and gene expressions.

Methodology:

1.) Find a partner and give them a coin that
has both a "heads" and a "tails" side.

2.) At the same time, you and your partner
should flip your coins, noticing which side lands face up.

3.) Whenever you or your partner's coin
lands "heads" side up, record it in the chart provided as the letter
"B", the dominant allele. Whenever the coins land "tails" side up,
record it as the letter "b", the recessive allele. Always record the
letters in the same order, for example, if you record your toss first
and your partner's second, always record the tosses in that order.
Remember that a combination of "Bb" and "bB" is the same.

4.) Repeat steps 2 and 3 for forty tosses.

5.) When you have forty tosses completed and
filled in the chart, count the number of each group of pairs that you
recorded &endash; this will end up as three totals: one for number of
"BB" tosses, one for "Bb" tosses, and one for "bb" tosses.

6.) Compare these results with the expected
total of genes as shown in the second Punnett square
above.

7.) Do these result's match up with the
expected probability? Why or why not?

Misc. Helpful Information/ Hints/
Suggestions:

Recreate this chart to allow the students to
keep track of their tosses:

Gene Frequency:

Number of "BB" tosses (heads + heads) Number
of "Bb" or "bB" tosses (heads + tails) Number of "bb"
tosses

(tails + tails)

Total tosses: ---________ Total tosses:
________ Total tosses: ________

Gene Expression:

- Add the totals from the first two columns
to find the total number of genes that would express the dominant
gene.

- Divide these totals by forty to get the
frequency of occurrence in the population.